1. Technical Field
The present invention relates to Active Engine Mounts (AEM) and methods of counteracting engine produced noise and vibration. More particularly, the present invention relates to an improved AEM system that integrates an open-loop control algorithm with a tunable closed-loop control algorithm to result in a rapidly responsive, adaptive and robust combination system.
2. Discussion of Prior Art
Electro-hydraulic devices, such as Active Engine Mount (AEM) systems have long been developed to counteract engine produced noise and vibratory forces. Recently, these devices and systems have become increasingly vital, as engine designs have endeavored to provide increased fuel efficiency at the cost of also increasing generative vibratory by-product. For example, Active Fuel management (AFM) engines, which function to autonomously deactivate half of the cylinders of an internal combustion engine during cruising, and the higher firing forces and cycles associated therewith have resulted in higher torque variations and, in turn, higher levels of structural vibrations.
Intermediately positioned between the engine and adjacent structure, AEM systems have traditionally included a passive spring and damper combination that isolate the adjacent structure from these static and dynamic loads. As shown in prior art FIG. 1, recent AEM systems 1 have further included a generator 2, such as a solenoid, voice coil, or other electromagnetic device. When active, the generator 2 receives an instructive signal and produces a counteractive output (i.e., restoring force) based on the signal. The output resultantly isolates the vibrations that would be otherwise transmitted from the engine to the adjacent structure.
In one type of conventional AEM system, the signal is pre-determined and produced by an open-loop controller, and is typically a function of vehicular and/or engine specific characteristics. This type of system provides a rapid-response dampening effect, as shown in the exemplary open-loop output graph of FIG. 2. In this simulation, the open-loop AEM system was activated at a time 0.5 sec to enable comparisons between pre-and-post-activation. A residual vibration resulted after the control was activated, which took into effect modeling error inserted into the open-loop algorithm to simulate un-modeled disturbances, intra-vehicular degradation over time, and inter-vehicular variations amongst different makes and models. It is appreciated that these errors almost always result in measurable inaccuracy within an open-loop control system.
To enable AEM systems to achieve their overall final control objective more consistently, closed-loop systems have been developed that utilize sensory feedback to improve performance. This type of system typically includes a plurality of sensors (one at each engine mount) that sense and generate a correlative signal of noise and vibration occurring at the engine mount. The sensor feedback is used to modify the input signal to the generator 2, and accordingly converge the residual vibration towards a targeted threshold. As a result, a more robust and adaptive system is presented.
While improving isolation, however, conventional closed-loop AEM control algorithms present inferior response times in comparisons to open-loop systems. This is shown in the closed-loop simulation output graph of FIG. 3. As detected by the model, an incipient activation period of high vibration results, which presents repetitive opportunity for compromising structural integrity, and creating operator discomfort. Of further concern, it is further appreciated that such a period will occur during each change in rpm or engine torque.
Thus, AEM systems are becoming increasingly necessary, however, they continue to present adaptivity and responsiveness concerns associated with open and closed-loop variations, respectively. As a result, there remains a need in the art for a rapid response AEM system that provides robust and adaptive control capabilities.